It's a lot. Maybe too much.
Here's the uncomfortable truth: most of these metrics don't change how you coach. They're interesting, occasionally useful, but rarely actionable. You glance at them, nod, and go back to doing what you were already doing.
But a few metrics genuinely matter. They answer specific coaching questions that used to require expensive lab tests or pure guesswork. Two of them—Aerobic Efficiency and Cardiac Drift—deserve a permanent spot in your coaching workflow. And then we'll talk about when to ignore numbers entirely.
The problem with most metrics
Ten years ago, coaches complained about not having enough data. Now we're drowning in it.
The average GPS watch tracks 30-50 variables per workout. Coaching platforms display charts, graphs, trends, and comparisons. Athletes ask about metrics they read about on Reddit. Everyone wants to optimize something.
But more data doesn't make you a better coach. What matters is having metrics that answer real questions—questions that actually influence your training decisions.
Questions like:
- Is my athlete's aerobic base genuinely improving, or are we just accumulating miles?
- Is this athlete recovered enough for tomorrow's hard session?
- Should I back off this week, or push through?
Most metrics can't answer these. The two below can.
Metric #1: Aerobic Efficiency (AE)
What it is
Aerobic Efficiency measures how fast your athlete can run at their aerobic threshold heart rate. Simple concept: as fitness improves, they run faster at the same heart rate.
You probably know this intuitively. A well-trained athlete cruises at 5:00/km with a heart rate of 145. A less fit version of the same athlete runs 5:30/km at that same 145 bpm. The pace at threshold heart rate—that's Aerobic Efficiency.
The coaching question it answers
"Is my athlete's aerobic base actually improving?"
This is the question that used to require lab tests. Lactate threshold testing, VO2max assessments, metabolic carts—all expensive, all inconvenient, all giving you a snapshot from one day that may or may not reflect reality two weeks later.
AE gives you the answer from regular training data. No lab required. No special test workouts. Just consistent tracking from the runs your athlete is already doing.
Why this matters for coaches
When an athlete asks "Am I getting fitter?", you need more than "I think so" or "Your long runs feel easier." AE gives you a number. A trend. Proof.
More importantly, it tells you when aerobic development has stalled. If AE flatlines for 4-6 weeks despite consistent training, something needs to change. More volume? Different intensity distribution? More recovery? The metric won't tell you what to fix, but it will tell you that fixing is needed.
How to use it in practice
AE works best with steady-state runs—long runs, easy runs, tempo efforts on flat terrain. The key is consistent pace with naturally varying heart rate. Not intervals. Not heart-rate-controlled zone sessions where pace fluctuates while HR stays locked.
In Good Coach App, AE calculates automatically for qualifying workouts. You'll see the pace your athlete would run at their aerobic threshold, plus a confidence indicator showing how reliable the calculation is.
Check it monthly for trends. A well-designed aerobic block should show 2-5 seconds per kilometer improvement each month. If you're seeing that, the training is working. If not, you have a real data point to drive your next conversation.
Metric #2: Cardiac Drift
What it is
Cardiac Drift is the percentage increase in heart rate during sustained exercise at constant effort. You've seen it happen: an athlete runs steady 5:15/km pace for an hour. First half average HR: 142. Second half average HR: 151. That's cardiac drift—about 6.3% in this case.
It happens because the body works harder to maintain the same output over time. Blood volume decreases (sweating), core temperature rises, cardiovascular system compensates by beating faster.
The coaching question it answers
"Is my athlete recovered, hydrated, and ready for hard training?"
This is a daily question, and until recently, coaches answered it through subjective feel—asking athletes how they slept, how their legs feel, whether they're stressed. That works, but athletes aren't always accurate reporters of their own readiness.
Cardiac drift gives you an objective signal. High drift suggests something's off—dehydration, accumulated fatigue, poor recovery, heat stress, or sometimes early illness. Low drift means the system is running efficiently.
Why this matters for coaches
Cardiac drift is your early warning system. It often shows problems before the athlete feels them.
A coach managing 20+ athletes can't have a 15-minute readiness conversation with each one every day. But you can scan cardiac drift values in two minutes and spot who needs attention. The athlete showing 12% drift three workouts in a row? That's your Monday phone call. Something's happening—overtraining, life stress, inadequate fueling—and you caught it before it became an injury or burnout.
The three things cardiac drift tells you
Hydration status. Dehydrated athletes show higher drift because blood volume drops, forcing the heart to work harder. Consistent high drift often fixes itself when athletes improve their hydration habits.
Heat adaptation. Athletes new to hot conditions show elevated drift. As they adapt over 1-2 weeks, drift normalizes. This helps you gauge when an athlete is ready to resume normal training intensity after a climate change.
Recovery state. Accumulated fatigue shows up as drift before it shows up as performance decline. An athlete in a hard training block whose drift creeps from 4% to 8% to 11% over three weeks? Time for a recovery week.
How to use it in practice
In Good Coach App, cardiac drift calculates automatically for steady-state endurance workouts—any sustained effort of 30+ minutes without intervals. You'll see the percentage and a quality rating (excellent, acceptable, or poor).
Here's a simple framework:
- Under 5%: Excellent. Athlete is well-recovered and well-hydrated.
- 5-10%: Acceptable. Normal for longer efforts or warmer conditions.
- Over 10%: Investigate. Check hydration, recovery, stress, or potential illness.
One high reading means nothing. Three in a row means something.
When to ignore the metrics
Now for the part most data-focused articles skip: sometimes the numbers don't matter.
Metrics tell you what happened. They can't tell you why. They can't capture the athlete who just went through a breakup, the one whose confidence is shot after a bad race, or the one who needs to feel fast more than they need to train smart.
The best coaches use metrics as conversation starters, not verdicts. "Your cardiac drift has been high lately—how are you feeling?" leads somewhere useful. "Your cardiac drift is high so we're cutting volume" might miss the actual issue entirely.
There are moments when human judgment beats data:
- Race day decisions when conditions change
- Athletes dealing with personal stress or major life transitions
- Motivation problems that no training adjustment will fix
- The gut feeling that something's off even when numbers look fine
A number on a screen will never know your athlete the way you do. The goal isn't to replace your coaching instincts with data. It's to inform those instincts, to catch things you might miss, and to confirm what you already suspected.
Metrics tell you what. The athlete tells you why. You need both.
A simple weekly workflow
You don't need to spend 30 minutes analyzing data for each athlete. Here's a minimal approach that captures most of the value:
Monday morning (5 minutes): Scan last week's cardiac drift values across your roster. Flag anyone with consistently high readings or upward trends.
After long runs: Check AE for athletes in aerobic development phases. Note the number. Compare to last month.
Monthly (15 minutes per athlete): Review AE trend over 4-6 weeks. Is it improving, flat, or declining? This drives your periodization decisions.
That's it. Five minutes daily, an hour monthly. The platforms do the calculations. Your job is interpretation and action.
The balance
Coaching endurance athletes in 2025 means navigating a flood of data. The temptation is either to obsess over every metric or to ignore them all and coach purely by feel.
Neither extreme serves your athletes.
The practical middle ground: track a few metrics that answer real coaching questions. Aerobic Efficiency tells you if the aerobic base is developing. Cardiac Drift tells you if the athlete is ready to train hard today. Both provide objective signals that complement—but never replace—your coaching judgment.
In Good Coach App, these metrics calculate automatically from synced workout data. No special tests, no extra work for athletes, no manual calculations. Just useful numbers appearing when the data supports them.
Use them as tools. Trust your instincts. Coach the human, not the dashboard.
Want to dive deeper into how these metrics work? Check out our full documentation on Aerobic Efficiency and Cardiac Drift.